Cortana is a Windows Phone virtual assistant that uses a Bing Predicts algorithm to pick a winner in every NFL game. The algorithm takes into account things like advanced stats and home-field advantage. There's also a public-perception component that uses Facebook data.

Cortana's 13-3 record made Week 15 its best week since Week 5, when it went 13-2. It picks games straight up, not against the point spread. Las Vegas betting favorites went 12-4 in Week 15, as did Nate Silver's ELO model.

On the season, ELO has predicted 69.6% correct, while Vegas favorites are right around Cortana at 65.6%.

The Bing Predicts algorithm that nailed the World Cup correctly predicted 15 of the tournament's last 16 games. We'll see if Week 15 is the beginning of another closing hot streak.